You can get 150's, 165's and many other bullet weights for the 300 weatherby, although, you may have to reload.
Make sure whatever you intend to shoot hunting you sight in with as different bullets shoot to different places, sometimes by a lot, just a change in brand of bullet in the same weight can make a huge difference. I have a 222 that is sighted in for 40 and 50 gr noslers, and if I switch to 50 gr winchesters it shoots almost 6 inches high and 6 inches right in a nice tight group.
As far as the screws coming loose, if they do, which they shouldn't, use loctite on them, the kind that you can still unscrew later.
Another option would be to install a muzzle break, or a mercury recoil reducer in the stock. Since it is inherited, i would assume it is older and may be worth a bit of money, so probably the best bet is the mercury recoil reducer in the stock. One note of warning on those, they do work, but they also change the balance of the gun.